FIG. 16 is a block diagram showing an optical communication unit according to, for instance, Japanese Patent Laid-Open Publication No. HEI 8-161089. The optical communication unit shown in FIG. 16 comprises a first communication unit 71 connected to a personal computer and functioning as an optical interface, and a second communication unit 81 connected to a printer and functioning as an optical interface.
These first communication unit 71 and second communication unit 81 are arbitrarily spaced therebetween according to each place where a personal computer and a printer are installed respectively, so that a distance of the space therebetween is a distance for spatial transmission of the infrared ray.
At first, the first communication unit 71 comprises a signal converting circuit 72 for converting electric signal data outputted from a personal computer to data for transmission with an infrared ray, an LED driver 73 for driving a light emitting diode (LED) 74 emitting an infrared ray, an LED 74 emitting an infrared ray, a photodiode (PD) 75 for receiving an infrared ray emitted by the LED 84 of the second communication unit 81, a detecting circuit 76 for detecting the infrared ray received by the PD 75 and obtaining data for the infrared ray, and a signal converting circuit 77 for converting the data for the infrared ray to electric signal data and transferring the electric signal data to the personal computer.
On the other hand, the second communication unit 81 comprises a signal converting circuit 82 for converting electric signal data outputted from a printer to data for transmission with an infrared ray, an LED driver 83 for driving an LED 84 emitting an infrared ray, an LED 84 emitting an infrared ray, a photodiode 85 for receiving an infrared ray emitted by the LED 74 of the first communication unit 71, a detecting circuit 86 for detecting the infrared ray received by the PD 85 and obtaining data for the infrared ray, and a signal converting circuit 87 for converting the data for the infrared ray to electric signal data and transferring the electric signal data to the printer.
Next description is made for the operations of the optical communication unit having the configuration as described above. In the optical communication unit shown in FIG. 16, when data is printed by a printer, an output signal processed by a personal computer is received by the signal converting circuit 72, and is converted to a serial signal for optical communication. When the converted serial signal is sent to the LED driver 73, the LED driver 73 blinks the LED 74 according to the converted serial signal and emits an infrared ray.
The outputted infrared ray by means of emission by the LED 74 is received by the PD 85 in the printer. The received infrared ray is further converted, when having been detected by the detecting circuit 86, to a signal for controlling the printer in the signal converting circuit 87 provided in the following stage. The signal for controlling the printer is outputted to the printer and processing for controlling the printer is started.
It should be noted that the same processing as that from the personal computer to the printer is executed also to an infrared communication from the printer to the personal computer but in the reverse order thereof.
The conventional type of optical communication unit, however, assumes spatial transmission as a communication mode, so that optical power is adjusted for a distance of spatial transmission by about 1 m. For this reason, when communication for a short distance (e.g. 0 m), namely so-called the contact communication is executed, the light in the light receiving side is much stronger than required, so that energy loss is large in the light emitting side. Further, a transmission speed of 4 Mbps is appropriate, from a view point of efficiency of using light energy, for the spatial transmission for 1 m, but the transmission speed is too slow in the contact communication even if a balance with the optical power is taken into considerations.